The invention relates to electrical position resolver arrangements, that is to say arrangements where the position of a probe relative to a surface across which the probe is movable is resolved and translated into electrical signals representative of the position of the probe.
Electrical position resolvers are known in which the surface is provided with a resistive layer to which connection is made by means of electrodes arranged around the periphery of the layer, there being four electrodes arranged in two pairs of parallel electrodes with the electrodes of one pair being perpendicular to those of the other.
It is known to produce across one or both pairs of the electrodes a uniform potential gradient and a voltage signal may be picked off by the movable probe to provide a signal amplitude that is indicative of the position of the probe. However such devices, utilising direct contact, can suffer from the disadvantage that contact resistance at the probe tip results in inaccurate indications of the position of the probe and, in the case of capacitative coupling, variations in the distance of the probe from the resistive layer (variations produced, for example, by the non-uniformity of thickness of the insulating layer normally provided over the resistive layer to protect the latter) will adversely affect accuracy due to signal amplitude variations.
Position resolving devices which do not suffer from these defects are also known, in which phase gradients are established across a uniform resistive layer by applying to opposite edges of the resistive layer alternating voltage signals of the same frequency but with a predetermined phase relationship between the signals. A probe which is movable with respect to the layer provides a signal, the phase of which is indicative of the position of the probe. With such a position resolving arrangement, the relationship between the phase of the signal at the probe and the position of the probe is non-linear when the alternating voltages applied to the edges of the resistive layer are of one frequency and essentially sinusoidal in waveform.
Further, it is usual in such systems employing sinusoidal waveforms to use circuits made resonant at the sinusoidal frequency in order to enhance the desired signal compared with any undesired noise signals which may be present. However, a considerable disadvantage when employing resonant circuits is the transient response time of amplitude or phase or amplitude and phase which results whenever the amplitude or phase is changed discontinuously.
It is an object of the invention to provide an improved electrical position resolver arrangement.